Gonadal steroid hormones regulate reproductive and social behaviors in many vertebrates. In several species it has been demonstrated that steroids effect behavioral changes by acting on the preoptic area of the hypothalamus. However, the mechanism(s) by which hormone stimulation induces behavioral change remains unknown. Hormones also influence social behaviors less directly by altering the social signals an animal produces which, in turn, alter the responses elicited from conspecifics. In mammals these hormone-dependent social signals are often odorous chemicals called pheromones. The literature on olfactory communication in mammals is increasing steadily, yet many basic questions remain unanswered and, again, the mechanism(s) by which olfactory perception of pheromones modifies behavior is unknown. The proposed research examines questions regarding hormonal and pheromonal control of behavior by studying scent marking, aggression and sexual behavior in Mongolian gerbils. Manipulations of steroid hormone levels by gonadectomy, systemic injections and intracranial application will be performed to determine to what extent these three behavior patterns can be distinguished in terms of their hormonal bases and of their neural sites of hormone control. The same techniques are also used to gather information on neural mechanisms of hormone action including specificity of steroid structure, the role of RNA synthesis and the effects of variations in neurotransmitter activity. Other studies employ stimulus generalization techniques to determine more precisely what pheromonal cues gerbils attend to in situations where odors are known to elicit specific behavioral responses.